Today I had my first crash at the beach. I live on a hill and is where I usually lift off. When I fly out to sea I have to lower my quad under 0m. I do this all the time but today something strange happened. My battery level indicator of the battery of the drone turned red at a level of 68%. So I ignored this. I kept on flying for couple more minutes before I guided the drone back home. This didn't work out well. I was not able to climb. My screen told me I was flying at an altitude of exact 20m, while in fact it was at something like 10m under me. Fortunately I was able to land it at the beach where I picked it up. Any ideas what was going on here? Is it a known issue? My setup is in NAZA mode with switch S1 fully up. Would another mode have helped?